The aim of this project was to evaluate the association between the genotype of candidate genes and presbyacusis by cross-section and case-control study. In the first stage, the investigators plan to select 700 healthy subjects older than 50 with symmetric, sensorineural hearing loss. The subjects will receive basic otologic examination, pure tone audiometry, questionnaire, and genotype analysis. Because gender and age would affect hearing loss significantly, The investigators will convert the hearing level of all subjects into a gender and age independent Z-score according to ISO 7029 standard. And, The investigators define subjects within higher 30 % of Z-score as the presbyacusis group, and subjects within lower 30% of Z-score as the control group. Finally, The investigators perform Chi square analysis to test the association between genotype of candidate genes or their combinations in both groups, and calculate the odds ratio for presbyacusis between different genotype of candidate genes. Further more, we will evaluate the effect of genotype of candidate genes, environment factors, and gene-environmental interaction on the severity of presbyacusis by multivariate logistic regression.